There are countless examples in nature of biological adaptations going hand in hand with either a nocturnal or diurnal (day-time) lifestyle. For instance, cats have reflective lenses allowing better vision in low light; chimps have colour vision which is useful for spotting fruit in daylight.

In a new paper Peter Jonason and his colleagues provide evidence that in humans certain personality types act as a form of adaptation that correlates with a preference for daily or nightly living (a person’s “chronotype”). Specifically the researchers have shown that people with a preference for the evening and night-time tend to score highly on the “Dark Triad” of personality traits – Machiavellianism, psychopathy and narcissism.

Jonason and his colleagues surveyed 263 students online (average age 24; there were 74 men) using a narcissism scale (participants rated their agreement with statements like: “I have a natural talent for influencing people”); a psychopathy scale (e.g. “I think I could beat a lie detector”), a Machiavellianism scale (e.g. “it is hard to get ahead without cutting corners here and there”) and chronotype questionnaire (participants answered questions like “During the first half hour after you wake up in the morning, how do you feel?”).

Across the sample, average Dark Triad trait scores correlated negatively with chronotype scores (r was -.14, p<.001 where -1 would be a perfect correlation). That is, the darker a person’s personality score, the more they tended to be an “owl” and to say they functioned more effectively in the evening. Drilling down into the individual subscales: psychopathy, Machiavellianism, and the entitlement/exploitativeness aspects of narcissism all correlated on their own with eveningness on the chronotype questionnaire.

Jonason and his team said their results were consistent with a “niche-specialisation” hypothesis. “It could be adaptively effective for anyone pursuing a fast life strategy like that embodied in the Dark Triad to occupy and exploit a low-light environment where others are sleeping and having diminished cognitive functioning,” they said. “Such features of the night may facilitate the casual sex, mate-poaching, and risk-taking the Dark Triad traits are linked to.”

The findings give pause for thought but the dependence on a student sample once again raises questions about the generalisability of the results. The modest size of the relevant correlations also undermines the researchers’ theoretical speculations. Another problem is the reliance on self-report. This is common in chronotype research, but nonetheless it raises the issue of whether the self-described owls really do function better in the evening or if they simply prefer that time of day.